The present exemplary embodiment relates to a fuser apparatus for an electrophotographic marking device and, more particularly, to control of an operating temperature of a fuser apparatus.
In typical xerographic image forming devices, such as copy machines and laser beam printers, a photoconductive insulating member is charged to a uniform potential and thereafter exposed to a light image of an original document to be reproduced. The exposure discharges the photoconductive insulating surface in exposed or background areas and creates an electrostatic latent image on the member, which corresponds to the image areas contained within the document. Subsequently, the electrostatic latent image on the photoconductive insulating surface is made visible by developing the image with a dry marking material. Generally, the marking material comprises pigmented toner particles adhering triboelectrically to carrier granules, which is often referred to simply as toner. The developed image is subsequently transferred to the print medium, such as a sheet of paper.
The fusing of the toner image onto paper is generally accomplished by applying heat and pressure. A typical fuser assembly includes a fuser roll and a pressure roll which define a nip therebetween. The side of the paper having the toner image typically faces the fuser roll, which is often supplied with a heat source, such as a resistance heater, such as a lamp, at the core thereof. The combination of heat from the fuser roll and pressure between the fuser roll and the pressure roll fuses the toner image to the paper, and once the fused toner cools, the image is permanently fixed to the paper.
The paper passing through the fuser absorbs heat from the fuser roll. The temperature of the roll is measured by a thermistor and power is supplied to the resistance heater to maintain the fuser roll at a desired operating temperature. When narrow width paper is fed to the fuser, the side of the fuser roll which does not make contact with the paper tends to heat preferentially. In some fuser assemblies, the heater includes two lamps aligned parallel with the fuser axis, which preferentially heat different sides of the fuser roll. Each lamp is associated with its own control loop with a thermistor for measuring the temperature of the respective side of the fuser roll and controlling the lamp to maintain the desired temperature. Each of the feedback loops operates independently, ignoring the influence of one lamp on the temperature of the other side of the fuser roll, and vice versa. It has been found that, particularly for long print jobs employing relatively narrow paper, the temperature of the side of the fuser roll which does not make contact with the paper can reach unacceptably high levels. If the temperature of the fuser roll becomes too high, the fuser roll, or associated equipment, such as a web cleaning device, can be damaged. Accordingly, the printer is often cycled into a non-operational mode for a period of time to allow the fuser roll to reach a safe operating temperature.